An amino group-containing vinyl monomer is homo-polymerized or copolymerized with other vinyl monomer(s) and is widely used as a raw material for producing various amino group-containing vinyl polymers. An amino group-containing vinyl polymer is utilized in various fields, for example, as a coagulant, a dispersing agent, an additive to a papermaking stock, a polymer for recovery of petroleum, a vehicle for coating paints, an adhesive and others.
Hitherto, as an amino group-containing vinyl monomer, an N,N-dialkylaminoalkyl(meth)acrylate has widely been utilized. Recently, however, an N,N-dialkylaminoalkyl(meth)acrylamide of the following general formula (II) has been considered important because of the excellent hydrolysis-resistance and the excellent hydrogen-bonding ability of the amido group. ##STR3## where R.sub.3 represents a hydrogen atom or a methyl group;
R.sub.4 and R.sub.5 independently represent an alkyl group having from 1 to 4 carbon atoms; and PA1 n represents an integer of from 2 to 4. PA1 R.sub.4 and R.sub.5 independently represent an alkyl group having from 1 to 4 carbon atoms; and PA1 n represents an integer of from 2 to 4.
However, N,N-dialkylaminoalkyl(meth)acrylamides have a problem in that the storageability thereof is poor, although they have the above-mentioned various excellent characteristics. Precisely, N,N-dialkylaminoalkyl(meth)acrylamides have a severe problem in that they are deaminated with the lapse of time under the condition of contact with oxygen to give divinyl impurities as by-products.
For instance, when N,N-dimethylaminopropylacrylamide is allowed to stand in air for a while, it gives a divinyl impurity of allylacrylamide as a by-product in an amount of several hundred ppm in one month.
Where the thus by-produced divinyl impurity-containing N,N-dialkylaminoalkyl(meth)acrylamide is polymerized, the solubility of the resulting polymer in solvents would be worsened or the viscosity of the polymer would disadvantageously increase, because of the crosslinking reaction occurring along with polymerization reaction. As a result, the polymer to be formed is to have some undesirable property which is different from the originally intended property, and such undesirable property often causes some serious problems in practical use of the polymer. In particular, when a water-soluble polymer having a high molecular weight is to be obtained, there would occur a fatal problem in that the polymer formed could not dissolve in water. Though depending upon the molecular weight of the polymer to be formed, the solubility of the polymer is generally worsened when the content of the divinyl compound impurity in the polymer is 10 ppm or more.
On the other hand, conventional N,N-dialkylaminoalkyl(meth)acrylamides color with the lapse of time in the presence of oxygen. Coloration extremely lowers the commercial value of polymer products to be obtained from the monomers. In particular, it causes a serious drawback in that the colored polymers cannot be used in a field where the appearance color of products is an important factor. Under the such situations the utilizable range of N,N-dialkylaminoalkyl(meth)acrylamides is often restricted because of the undesirable coloration of the monomers.
For overcoming the above-mentioned problems of by-production of divinyl compounds and coloration of monomers, there are known a method of polymerizing the monomers immediately after preparation or purification of the monomers, and a method of storing the monomers under the condition of an extremely low temperature. However, these methods are not industrially practicable. On the other hand, a method of minimizing the contact of an N,N-dialkylaminoalkyl(meth)acrylamide with oxygen so as to prevent by-production of divinyl impurities has been proposed (Japanese Patent Application Laid-Open No. 63-270653). However, control of the method is complicated and the method is accompanied by a dangerous possibility that the monomer will be polymerized. Therefore, the utilizable range of the method is limiting.
As mentioned above, dialkylaminoalkyl(meth)acrylamides which have an excellent storageability under a general storage condition and which are free from a problem of polymerizing are desired in this technical field.